Unless otherwise indicated herein, the description in this section is not prior art to the claims in this application and is not admitted to be prior art by inclusion in this section.
A typical image forming apparatus such as a copier and a printer includes a fixing device that fixes a toner image transferred on a paper sheet on the paper sheet. A fixing device includes a fixing roller and a pressure roller that form a fixing nip by being brought into pressure contact with one another. A toner image undergoes heating and pressurization to be fixed on a paper sheet when the paper sheet passes through the fixing nip.
In such a fixing device, a paper sheet sometimes winds around a fixing roller after passing through a fixing nip. Accordingly, to prevent winding of the paper sheet, the fixing device includes a separating member that separates the paper sheet from the fixing roller after the paper sheet passes through the fixing nip. The separating member includes a separation plate that faces an outer peripheral surface of the fixing roller and a contact member that holds the separation plate with a predetermined clearance from the outer peripheral surface. The contact member forms the clearance between the separation plate and the outer peripheral surface by being brought into contact with the outer peripheral surface in a non-paper passing region, which is outside a paper passing region of the fixing roller.
Thus, since the contact member always contact the fixing roller, the contact portion with the contact member of the fixing roller fiercely wears. Use of an IH as a heat source may cause a fixing member to be driven even during waiting because of heat equalization for the fixing roller and thus may cause wear to further progress. In view of this, a fixing roller using a fixing belt causes a failure of the fixing belt.
Meanwhile, passing a special paper such as an envelope requires reduction of a fixing pressure of the fixing nip. In view of this, the fixing roller and the pressure roller are separably located such that the fixing pressure is switchable between a pressurized state and a reduced pressure state. Even in such reduced pressure state, a predetermined clearance needs to be allocated between the outer peripheral surface of the fixing roller and the separation plate. An unstable clearance may cause a paper-passing-through failure where a distal end of an envelope is caught by a distal end of the separation plate.
There is known a fixing device configured to separate a contact member from a fixing roller during switching a fixing pressure from a pressurized state to a reduced pressure state. This fixing device is configured to switch the fixing pressure by moving the fixing roller with respect to the pressure roller. Then, during movement of the fixing roller in switching of the fixing pressure from the pressurized state to the reduced pressure state, a movable frame that supports the fixing roller interferes with the contact member to separate the contact member from the fixing roller.